The present invention relates to a side airbag apparatus that protects an occupant seated in a vehicle seat from an impact by deploying and inflating an airbag on a side of the occupant when the impact is applied to the vehicle.
A side airbag apparatus having an airbag and an inflator is effective as an apparatus that protects an occupant seated in an automobile seat when an impact is applied to the seat from a side, for example, due to a side collision. One known form of the side airbag apparatus includes an airbag having an airbag main body, which forms the outer envelope, and a lateral partition, which is provided in the airbag main body in a bridging manner (for example, Japanese Laid-Open Patent Publication 2011-126497). The lateral partition of this side airbag apparatus divides the interior of the airbag main body into an upper inflation chamber above the lateral partition and a lower inflation chamber below the lateral partition.
When an impact is applied from the side to a body side portion of the automobile, for example, to a side door, the inflator supplies inflation gas to the upper inflation chamber and the lower inflation chamber. At this time, the amount of the inflation gas supplied to the lower inflation chamber is greater than the amount of the inflation gas supplied to the upper inflation chamber. The upper inflation chamber is deployed and inflated between a part of the occupant's body above the lumbar region and the inwardly bulging body side portion. The lower inflation chamber is deployed and inflated between the occupant's lumbar region and the body side portion with an internal pressure higher than that of the upper inflation chamber. Thus, the lumbar region, which has a higher impact resistance than the thorax region, is pushed by the lower inflation chamber, which is inflated with a high internal pressure. Also, the thorax region, which has a lower impact resistance than the lumbar region, is pushed by the upper inflation chamber, which is inflated with a lower internal pressure than that of the lower inflation chamber. As a result, the lumbar region and the thorax region are respectively restrained by the lower inflation chamber and the upper inflation chamber, which are inflated with a pressure distribution appropriate for the impact resistances of these regions, and the impact transmitted from the side to the occupant through the body side portion is reduced.
To protect an occupant from an impact with a side airbag apparatus, it is important that the amount of energy absorbed by the airbag be great. To that end, it is effective to increase the internal pressure of the upper inflation chamber and the lower inflation chamber and to inflate the inflation chambers largely in the widthwise direction of the automobile seat, that is, to increase the inflated dimension of each inflation chamber in the widthwise direction of the automobile seat.
In this regard, the side airbag apparatus of the above described document deploys and inflates the lower inflation chamber with a higher internal pressure than that of the upper inflation chamber. This allows the lower inflation chamber to absorb a sufficient amount of energy to effectively protect the lumbar region from an impact. However, since the upper inflation chamber is deployed and inflated with a lower internal pressure than that of the lower inflation chamber, the upper inflation chamber cannot easily exert the same effect as the lower inflation chamber. Further, the inflated dimension of the upper inflation chamber in the widthwise direction of the automobile seat is restricted by the lateral partition. Thus, there is still room for improvement in increase in the energy absorption amount of the upper inflation chamber to improve the protection performance for the thorax region.